Size of array of std::vector

Question

I would like to check the size() or number of rows in an array of std::vector().

I have vector like

std::vector<int> vec[3];

vec.size() does not work with the above vector declaration.

Answer 1

As for why vec.size() does not work, it's because vec is not a vector, it's an array (of vectors), and arrays in C++ are not objects (in the OOP sense that they are not instances of a class) and therefore have no member functions.

If you want to get the result 3 when doing vec.size() then you either have to use e.g. std::array:

std::array<std::vector<int>, 3> vec;
std::cout << "vec.size() = " << vec.size() << '\n';  // Will output 3

Or if you don't have std::array then use a vector of vectors and set the size by calling the correct constructor:

std::vector<std::vector<int>> vec(3);
std::cout << "vec.size() = " << vec.size() << '\n';  // Will output 3